1. Field of the Invention
The invention relates to a web winding device and method, and more particularly, to a web winding device and method for winding a material web into a winding roll, with a winding bed that is defined by at least one driven first support roller and a second support roller.
2. Discussion of Background Information
In one of the last manufacturing steps before paper leaves the paper factory, the paper web must be rolled into a winding roll so that it can be transported and above all, can be handled by a user.
A simple winding device of this type is the so-called support roller winder. Here, the winding roll rests on two (or more) support rollers. When one support roller is driveably rotated, the support roller simultaneously drives the winding roll along the circumference of the winding roll. Through rotation of the winding roll, the material web is drawn onto the winding roll. Although the diameter of the winding roll is increased in this process, this increase is not problematic since the center or the roll core of the winding roll can be moved from the support rollers.
A web winding device of the type mentioned above is known from DE 87 17 259 U1. With a winding device of this type, there exists the risk that air will get trapped between the layers of the winding roll. To prevent this, in one embodiment, the surfaces of the first support roller are provided with an elastic cover. In another embodiment, the winding device is embodied not as a double web winder, but as a support drum roller. In this embodiment, the jacket of the carrying drum can have a perforation through which air between the incoming web and the carrying drum can be removed to prevent the web from lifting away from the drum.
Another web winding device is disclosed in EP 0 791 550 A2. In this device, one of the two support rollers is provided with a vacuum box, which is effective on a portion of the circumference of this support roller that is outside the winding bed. If the roll is changed, the beginning of the incoming material web must be secured and the vacuum must be switched on. The material web can then be transported to the winding bed with the aid of the vacuum. During winding, the vacuum is switched off and pressure is built up in the winding bed. This pressure urges the roll upward, thereby reducing the load of the roll on the support rollers.
In a winding roll, the proper progression of winding tightness is of great significance. Normally, a greater winding tightness is needed on the inside of the winding roll than in the outer layers. The winding tightness is influenced by a number of factors. One factor is the load pressure with which the winding roll rests on the support rollers. This rises as the roll diameter increases and thereby increases the winding tightness. Another factor is the tension with which the incoming material web is pulled onto the winding roll. The tension is influenced by the stations preceding the winding device, for example by a cutting device or other devices that can have a braking effect.
Winding tightness may be influenced by driving both support rollers or by means of different circumference speeds or drive moments. The tension in winding the individual layers onto the winding roll may be adjusted. Another method of influencing the winding tightness is by controlled the line load in the nip or roll gap between a support roller and the winding roll. With increasing roll diameter, the weight of the roll clearly increases and with it, the line load, i.e., the pressure with regard to the axial length. If precautions are not taken, this would lead to an increase in the winding tightness from the inside to the outside. However, such a progression is undesirable. Rather, decreasing the winding tightness from the inside to the outside is desirable. One possibility of reducing the line load involves building up pressure in the winding bed, for example in the form of an air cushion, which at least partially supports the winding roll so that the load pressure on the support rollers is reduced. However, in an embodiment of this kind, it must be assured that the winding bed can be sealed. On the one hand, the air losses should be kept low, yet, one must be able to increase the required pressure in the first place.